Interpretive Summary: For decades, soil fumigants have been used for the preplant control of plant parasitic nematodes in California vineyards. Methyl bromide (MBr) has been widely preferred due to its broad pest-control spectrum and high nematode control efficacy. However, MBr is an ozone-depleting molecule and is being phased out according to the provisions of the Montreal Protocol and U.S. Clean Air Act. Grapes, as an orchard replant in California, qualify for MBr critical use exemption (CUE). However, the number of CUEs is adjusted yearly based on decisions of the Parties to the Montreal Protocol and the U.S. Environmental Protection Agency and are expected to decrease over time. Vineyards are generally fumigated using tractor mounted shanks to deliver fumigants to the target depth. However, developments in drip fumigation technology have increased efficacy and reduced atmospheric emissions of some MBr alternatives in annual horticultural cropping systems and these tactics may also prove effective for perennial crops. In 2000, an experiment was initiated at the USDA ARS Research Center in Parlier, CA to test an integrated pest management approach for managing plant parasitic nematodes and other components of the grape replant disorder. We evaluated the combined effect of several shank- or drip-applied MBr alternatives and various nematode-tolerant or resistant rootstocks on the establishment and early yield of grapes replanted into a long-term vineyard site. Nematode data and grape yield were monitored for the first seven years of fruit production following fumigation. Although nematode populations were greatly influenced by the preplant fumigation treatments, relatively few impacts were noted on grape yield. Cumulative yield during the first four fruiting seasons ranged from 468 to 1164 lbs per eight-vine plot across all treatments and rootstocks. However, the use of preplant fumigants may still be required in replant vineyards where plant parasitic nematodes are known to be present.

Technical Abstract:
Preplant soil fumigation is a common practice to control plant parasitic nematodes to ensure uniform and healthy grapevine establishment in replant situations. An eight-year field study was conducted to evaluate a number of fumigation methods and rootstock effects on controlling soil pests and producing grapes after replant. The study revealed that 1,3-dichloropropene plus chloropicrin, iodomethane plus chloropicrin, and propargyl bromide generally controlled root-knot and citrus nematodes as well as methyl bromide over an 7-year evaluation period. Sodium azide and chloropicrin alone were less effective. After seven harvest seasons, cumulative fruit yield was not different among fumigation treatments. However, the effect of the fumigants on nematode control was very evident in the own-rooted “Thompson Seedless”. The “1103 Paulsen” rootstock was partially tolerant to root-knot and citrus nematodes for the first 3 to 4 years, respectively. In contrast, the rootstock “Freedom” proved to be a highly root-knot nematode resistant cultivar and kept soil nematode numbers relatively low regardless of fumigant treatment during the course of this experiment. Wherever possible the use of root-knot nematode-resistant rootstocks is encouraged.